From the publication DE10 2010 042 396 A1 a method for maintaining a predetermined voltage in a battery-supported electrical system of a vehicle during the operation of an electric starter motor is known. This conventional method includes the steps of: operating the electrical starter motor on the electrical system of the vehicle during a first period in series with a limiting resistor in order to limit the current flowing through the starter motor; and of operating the electric starter motor on the electrical system of the vehicle during a second period with a reduced limiting resistance in order to increase a power converted by the starter motor. Here, a transition from the first to the second period is controlled based on electrical characteristics sampled on the limiting resistor during the first period.